I have a TIVA TM4C1294NCPDT that uses ccs 6.1.2, TIRTOS 2.16.0.08, and compiler 5.2.7.
From the main before the RTOS starts, I call the function initAdc to init a ADC sequence that will read one sample from the ADC. The sample is a voltage that is converted into temperature.
void initAdc(void)
{
uint32_t pui32ADC0Value[1];
SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0); // enable the ADC device
ADCClockConfigSet(ADC0_BASE, ADC_CLOCK_SRC_PIOSC | ADC_CLOCK_RATE_HALF, 1); // set the clock.
ADCSequenceDisable(ADC0_BASE, ADC_SEQUENCE_NUMBER3_TEMP);
ADCSequenceConfigure(ADC0_BASE, ADC_SEQUENCE_NUMBER3_TEMP, ADC_TRIGGER_PROCESSOR, 0);
ADCSequenceStepConfigure(ADC0_BASE, ADC_SEQUENCE_NUMBER3_TEMP, 0, ADC_CTL_CH3 | ADC_CTL_IE | ADC_CTL_END );
ROM_ADCHardwareOversampleConfigure(ADC0_BASE, 64);
ADCSequenceEnable(ADC0_BASE, ADC_SEQUENCE_NUMBER3_TEMP); //enable the sequence
ADCIntClear(ADC0_BASE, ADC_SEQUENCE_NUMBER3_TEMP); //first clear the interrupt
ROM_ADCSequenceDataGet(ADC0_BASE, ADC_SEQUENCE_NUMBER3_TEMP, pui32ADC0Value); // flush the ADC
ROM_ADCSequenceDataGet(ADC0_BASE, ADC_SEQUENCE_NUMBER3_TEMP, pui32ADC0Value); // flush the ADC
ROM_ADCSequenceDataGet(ADC0_BASE, ADC_SEQUENCE_NUMBER3_TEMP, pui32ADC0Value); // flush the ADC
}//end short initAdc(void)
Once the RTOS starts, I periodically call the function every few seconds so it’s a slow rate.
unsigned long readAdcTemp(void)
{
unsigned long tempC;
static unsigned long data = 0, counter = 0;
float volts;
uint32_t pui32ADC0Value[1];
int32_t returnValue;
ROM_ADCProcessorTrigger(ADC0_BASE, ADC_SEQUENCE_NUMBER3_TEMP); // trigger the ADC to start a conversion
while(!ROM_ADCIntStatus(ADC0_BASE, ADC_SEQUENCE_NUMBER3_TEMP, false)) //poll till ADC is done converting
{
}
returnValue = ROM_ADCSequenceDataGet(ADC0_BASE, ADC_SEQUENCE_NUMBER3_TEMP, pui32ADC0Value); //read the ADC value
if(returnValue == 1)
{
data = pui32ADC0Value[0];
}
else
{
counter++;
printf("ADC error = %d, counter = %d\n", returnValue, counter);
}
volts = ((3.3) * (data)/(0xFFF));
tempC = (unsigned long) ( ( (volts / 2.0) - 0.424 ) * 160);
return (unsigned long) tempC;
} //end unsigned long readAdcTemp(void)
The software is working as expected for the most part but sometimes I get an error where ROM_ADCSequenceDataGet() returns a value of zero. For some stress testing I sped up the reading of the ADC from the task to call readAdcTemp() every 200mS and I ran it overnight and I saw about 4 times the ROM_ADCSequenceDataGet() returned a value of 0. I don’t know why this would sometimes fail to read the ADC.
Am I doing something wrong that would cause the ADC to sometimes not read?
Thanks,
Doug
